There are generally two types of body-implantable leads used with cardiac pacemakers, myocardial and endocardial. Myocardial leads presently require surgery to expose the myocardial tissue to which the electrode is affixed.
Endocardial leads have an electrode or electrodes located at the distal end and are inserted in and guided through a body vessel, such as a vein, into the heart where the electrodes contact, and in some cases, are secured to the heart through the endothelial tissue lining the heart interior. Endocardial leads are divided into active and passive fixation leads. Passive fixation leads are non-penetrating leads. Tines are an example of passive fixation leads. Active fixation leads are penetrating leads. Applicant's fixed screw lead is an example of an active fixation lead.
An important feature of an endocardial lead is that of having a means of securing the electrode to the heart without dislodgement. Active fixation leads reduce dislodgements. A disadvantage of prior art leads is that it may be difficult to know when the lead has been successfully embedded in the cardiac tissue. With a fixed screw lead, for example, it may be difficult to judge how many turns are necessary to embed or remove the helix without turning the lead too many times thereby causing undue trauma to the tissue. With such leads, the physician must tactilely determine the number of rotations necessary to achieve lead fixation. Proper lead fixation is important because if the screw or helix is not fully screwed into the tissue the lead may dislodge. On the other hand if the lead is screwed too much into the tissue the tissue may be damaged, possibly injuring the patient or impairing lead performance or both.
Endocardial screw-in type leads are well known in the art. For example, the U.S. Pat. No. 4,146,036 to Dutcher et. al discloses a unipolar fixed screw lead. With such leads, the physician tactilely determines the number of rotations necessary to achieve lead fixation.
U.S. Pat. No. 4,570,642 to Kane et al discloses an endocardial, unipolar, extendable screw-in lead. With such leads, the physician observes helix extension under fluoroscopy during lead fixation.
U.S. Pat. No. 3,974,834 to Kane et. al discloses an endocardial, bipolar, screw-in lead. With such leads, the physician tactually determines the number of rotations necessary to achieve lead fixation.
U.S. Pat. No. 4,046,151 to Rose discloses an endocardial, bipolar, screw-in lead. With such leads, the physician tactually determines the number of rotations necessary to achieve lead fixation.
U.S. Pat. No. 4,572,605 to Hess, discloses a typical connector assembly for a bipolar coaxial lead. With such leads, the physician tactually determines the number of rotations necessary to achieve lead fixation.
The use of fluoroscopy to detect longitudinal motion is well known in catheter art. See, U.S. Pat. No. 4,771,777 to Horzewski et al at col. 4, lns. 17-20.